Complex carbohydrates and polysaccharides have numerous functions in food products such as emulsifiers, emulsion stabilizers, thickening and gelling agents and suspending agents (Sandford, P. A. and Baird, J. (1983) "The Polysaccharides", Vol. 2. Aspinall, G.0. (ed), Academic Press, N.Y.). Most polysaccharides function by altering the properties of aqueous solutions or dispersions primarily via their ability to bind water molecules and ions; they also interact with each other through "junction zone" formation (Rees, D. A. (1972) Biochem. J. 126:257-273).
Several plant families include species that exude gums, and those that produce copious quantities represent a ready supply of gums. In addition to exudate gums, gums are also obtained from seeds, for example, guar gum, and from algae, e.g., agar. Gums produced as plant exudates or as extracts from seed or other plant materials can require manual harvesting and production can vary with climate and weather conditions.
Gums have been produced by bacterial fermentation under controlled conditions, and xanthan gum which is produced in this manner has recently achieved commercial significance. In general, these gums or mucilages are carbohydrate-enriched polymers of high molecular weight composed of acidic and/or neutral monosaccharide building units joined by glycosidic bonds. One disadvantage associated with xanthan gum production is that, because Xanthamonas campestris is a plant pathogen (Schaad N. W. (1982) Plant Disease 66(10):882-890), disposal of cells can present a problem.
Gum arabic is the dried exudate from species of the acacia tree (Acacia senegal) found in various tropical and semitropical areas of the world. The acacia trees produce large quantities of gum arabic under adverse conditions, i.e., lack of moisture, poor nutrition and high temperatures. The gum is collected as a natural exudate from the surface of wounds generally produced deliberately in cultivated trees. The exudate is dried to form a product which is graded by its color and contamination with dirt or foreign bodies such as wood or bark (Van Nostrand's Scientific Encyclopedia, 7th ed. (1989) D. Considine (ed.) Vol. I, p. 1389). The dried exudate is completely soluble in hot or cold water, yielding a viscous solution of mucilage finding wide use as an emulsion stabilizer and texture modifier in a wide range of foods, beverages and confectionery and also in adhesives, inks, textiles, printing and cosmetics.
Suspension-cultured plant cells secrete a mixture of complex carbohydrates and glycoproteins into the culture medium. The major classes of complex carbohydrate polymers are proteoglycans (e.g., arabinogalactan-proteins (AGPs)), polysaccharides (e.g., neutral and acidic pectins), hetero-and homo-glucans, heteroxylans, and hetero- and homo-mannans (McNeil et al. (1984) Ann Rev. Biochem. 53:625-663).
Plants of many plant families can be taken into callus (solid) culture and then into liquid suspension culture. It is known that AGPs and other complex carbohydrates and proteins are secreted by many such cell lines (Clarke et al. (1979) Phytochemistry 18:521-540; Fincher et al. (1983) Ann. Rev. Plant Physiol. 34:47-70).